The Protestant work ethic - less commonly the Puritan work ethic - is a Calvinist value emphasizing the necessity of constant labor in one's calling as a sign of personal salvation. Protestants beginning with Martin Luther had reconceptualized work as a duty in the world for the benefit of the individual and society as a whole. The Catholic idea of good "works" was transformed into an obligation to work diligently as a sign of grace.

The term was first coined by Max Weber who was the “youngest” of the German Historical School. The Protestant work ethic is often credited with helping to define the societies of Northern Europe and other Protestant countries where Protestantism was strong, such as in Scandinavia, Northern Germany, Great Britain and the U.S.. In such societies it is regarded by many observers as one of the cornerstones of national prosperity. It has been said that people in countries with Protestant roots tend to be more materialistic, perfectionist, and that they focussed more on work, compared to people many other countries, such as Spain and Italy, where the people had a more relaxed attitude toward work.

The notion faced some criticism in the twentieth century. The strongest such criticism was that it revolved mostly around the culture and history of Europe so did not take into account societies that had never been Christian of any type. Examples often cited are East Asian nations like Japan which have a strong work ethic, but never had more than a small minority of Protestants. Others feel that the recent economic progress of Catholic nations like Ireland makes the term at best of historical use. The capitalist development of Catholic northern Italy and south western Germany before and during the Protestant Reformation is also cited as a counter argument that other factors, including geographical and political ones, were the main drivers for capitalist development, not Protestantism per se. Similarly, the deep economic factors that gave rise to capitalist accumulation and development existed in Europe prior to the Reformation in 1517 and owe little to any religious factor, but more to the unravelling of feudalism and the functioning of governance institutions that strengthened property rights and lowered transaction costs.

A counter-argument is that "The Protestant work ethic" refers to its Protestant origin and does not require Protestantism itself. As Ireland was ruled by a Protestant nation, while Japan modelled its modernization on largely Protestant nations like the United States and Germany, they could have received the secularized ethic from Protestants without it accepting any religious underpinning to it. Similarly, successful capitalist countries with large Catholic minorities such as the United States, Canada, Australia, United Kingdom and New Zealand tend to be ignored in the analysis and lumped together as Protestant, despite the strong influence and 'capitalist outlook' of Catholics in the business community in all of these countries.